1. Field of the Invention
This invention relates to monitoring fuel pressure in a heating system. More particularly, this invention relates to monitoring fuel pressure sensors in a heating system.
2. Description of the Prior Art
Industrial heating systems such as ovens, furnaces, and boilers generally have a combustion chamber which is provided with fuel by a fuel main. However, before the fuel reaches the combustion chamber, it typically enters a system of valves, sensors and regulators which is known as a valve train.
In order to achieve proper combustion in the combustion chamber, the fuel pressure at the point where the fuel enters the combustion chamber must be regulated. If, for example, the fuel is gas, and the gas fuel pressure is too high, it is entering the combustion chamber at a very high rate. Therefore, there is less oxygen in the combustion chamber and a fuel-rich environment is created in the combustion chamber. At some point, the gas-to-oxygen ratio will reach a level where there is not enough oxygen present to cause combustion in the combustion chamber. In that case, uncombusted fuel will be pouring into the combustion chamber. This can create a hazardous and explosive condition.
If the gas pressure is too low at the point where it is entering the combustion chamber, the gas-to-oxygen ratio will fall below desired levels. Since there is plenty of oxygen in the combustion chamber, an air-rich environment is created which is nonexplosive. However, the environment in the combustion chamber can become so air-rich that the firing rate (i.e., the rate at which an air-fuel mixture is supplied to the combustion chamber) is not economical for the particular application of the heating system. Also, the environment in the combustion chamber can become so air-rich that there is not even enough fuel for combustion to occur. In either of these cases, it is desirable to be aware of the low fuel pressure and to remedy it.
Until now, it has been customary to use electromechanical pressure switches as limit switches for gas and oil pressures which directly de-energize fuel valves upon detecting a pressure out of limits. However, these create certain problems. Since fuel of any type has mass, and since there is pipe friction to overcome when the fuel flows through a pipe (e.g. gas main), transient pressure changes in the gas main can result from abrupt fuel flow velocity changes which occur, for example, when fuel valves are rapidly opened or closed. Pressure regulators currently used in valve trains have delayed response to flow velocity changes. Therefore, the electromechanical pressure switches often create nuisance shut-downs as a result of responding to the transient pressure changes that occur when fuel valves are opened and closed.
One way which has been used to avoid these nuisance shut-downs is to set pressure limits in the electromechanical pressure limit switches wide enough to accommodate the transient pressure changes. This is undesirable because the pressure limits may need to be set wider than those required by the heating system for proper combustion.
Therefore, there is a need to accommodate the transient pressure changes resulting from abrupt fuel flow velocity changes that occur as a result of fuel valves being opened and closed. These transient pressure changes need to be accommodated without sacrificing proper combustion in the combustion chamber.